Portable electric tool

ABSTRACT

A portable electric tool includes an output shaft extending in an axial direction and configured to be rotatable, a tool accessory configured to perform an eccentric circular motion according to the rotation of the output shaft, a dust collection fan fixed to the output shaft so as to circumferentially surround the output shaft, a motor disposed on an opposite side of the dust collection fan from the tool accessory in the axial direction and configured to provide a rotational driving force to the output shaft, a motor cooling fan disposed between the dust collection fan and the motor in the axial direction, a first weight attached to one of the dust collection fan and the motor cooling fan and having a specific gravity higher than the one of the fans, and a second weight disposed at a position different from the first weight in the axial direction.

TECHNICAL FIELD

The present invention relates to a portable electric tool.

BACKGROUND

As portable electric tools, orbital sanders have been known conventionally. The orbital sanders cause a pad coupled at one end of an output shaft (for example, a motor shaft) to perform an eccentric circular motion (an orbital motion). Sanding paper is attached to the pad. A sanding/abrading operation can be performed by pressing the sanding paper against a processing target.

On such orbital sanders, a vibration is generated according to the eccentric circular motion of the pad. A static unbalance or a couple unbalance is solved by directly or indirectly mounting a weight (a counterweight) on the output shaft to reduce such generation of a vibration. For example, Japanese Patent Application Public Disclosure No. 2013-188804 discloses a fan attached to an output shaft and including two thick portions that function as weights. This fan has a function as a dust collection fan and a function as a motor cooling fan.

SUMMARY

The present disclosure discloses a portable electric tool. This portable electric tool may include an output shaft, a tool accessory, a dust collection fan, a motor, a motor cooling fan, a first weight, and a second weight. The output shaft may extend in an axial direction and be rotatable. The tool accessory may be configured to perform an eccentric circular motion according to the rotation of the output shaft. The dust collection fan may be fixed to the output shaft so as to circumferentially surround the output shaft. The motor may be disposed on an opposite side of the dust collection fan from the tool accessory in the axial direction and be configured to provide a rotational driving force to the output shaft. The motor cooling fan may be disposed between the dust collection fan and the motor in the axial direction. The first weight may be attached to one of the dust collection fan and the motor cooling fan and may have a specific gravity higher than the one of the fans. The second weight may be disposed at a position different from the first weight in the axial direction.

According to this configuration, the first weight and the second weight are disposed at axially different positions, and therefore centrifugal forces respectively applied to the first weight and the second weight can be prevented from being canceled out by each other. Therefore, the masses of the first weight and the second weight required to solve a couple unbalance can be reduced. In addition, a large difference in specific gravity can be secured between the first weight and the one of the fans (the dust collection fan or the motor cooling fan) to which the first weight is attached, and the centrifugal force required to solve the couple unbalance can be efficiently generated. Therefore, the size of the first weight can be reduced. Furthermore, the weight of the one of the fans to which the first weight is attached can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a sander according to a first embodiment.

FIG. 2 is a left side view of the sander.

FIG. 3 is a plan view of the sander.

FIG. 4 is a cross-sectional view taken along a line A-A illustrated in FIG. 3 .

FIG. 5 is a partial enlarged view of FIG. 4 .

FIG. 6 is a partial cross-sectional view taken along a line B-B illustrated in FIG. 3 .

FIG. 7 is a perspective view of the sander with a part of components removed therefrom.

FIG. 8 is a perspective view of a dust collection fan, a motor cooling fan, a first weight, and a second weight.

FIG. 9 is a perspective view of the dust collection fan, the motor cooling fan, the first weight, and the second weight.

FIG. 10 is a perspective view of the dust collection fan, the motor cooling fan, the first weight, and the second weight.

FIG. 11 is a schematic view illustrating a layout of the first weight and the second weight according to a second embodiment.

FIG. 12 is a schematic view illustrating a layout of the first weight and the second weight according to a third embodiment.

FIG. 13 is a schematic view illustrating a layout of the first weight and the second weight according to a fourth embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Representative and non-limiting specific examples of the present invention will be described in detail below with reference to the drawings. This detailed description is merely intended to teach a person of skill in the art details for practicing preferred examples of the present invention and is not intended to limit the scope of the present invention. Furthermore, each of additional features and inventions disclosed below can be utilized separately from or together with the other features and inventions to provide further improved apparatuses and methods for manufacturing and using the same.

Moreover, combinations of features and steps disclosed in the following detailed description are not necessary to practice the present invention in the broadest sense, and are instead taught merely to particularly describe a representative specific example of the present invention. Furthermore, various features of the above-described and the following representative examples, as well as various features recited in the independent and dependent claims below, do not necessarily have to be combined in herein specifically exemplified manners or enumerated orders to provide additional and useful embodiments of the present invention.

All features disclosed in the description and/or the claims are intended to be disclosed separately and independently from each other for the purpose of original written disclosure, as well as for the purpose of restricting the claimed subject matter, independent of the compositions of the features in the embodiments and/or the claims. In addition, all value ranges and indications of groups or aggregations are intended to disclose every possible intermediate individual forming them for the purpose of original written disclosure, as well as for the purpose of restricting the claimed subject matter.

In one or more embodiment(s), the first weight and the second weight may be disposed so as to be spaced apart from each other in the axial direction via a spacer. According to this configuration, a great distance can be secured between the first weight and the second weight in the axial direction due to the spacer. Therefore, the masses of the first weight and the second weight required to solve the couple unbalance can be further reduced.

In one or more embodiment(s), the dust collection fan and the motor cooling fan may be disposed so as to be spaced apart from each other in the axial direction. This configuration allows the motor cooling fan to be disposed closer to the motor. Therefore, the motor cooling performance by the motor cooling fan can be improved.

In one or more embodiment(s), the dust collection fan and the motor cooling fan may be disposed so as to be spaced apart from each other in the axial direction via the spacer. According to this configuration, the dust collection fan and the motor cooling fan can be spaced apart from each other by a great distance. Therefore, the motor cooling fan can be located further closer to the motor and the motor cooling performance can be further improved.

In one or more embodiment(s), the first weight may be attached to the dust collection fan and may have a specific gravity higher than the dust collection fan. The motor cooling fan may be fixed to the output shaft so as to circumferentially surround the output shaft. The second weight may be attached to the motor cooling fan and may have a specific gravity higher than the motor cooling fan. According to this configuration, a large difference in specific gravity can be secured both between the first weight and the dust collection fan and between the second weight and the motor cooling fan, and the centrifugal forces required to solve the couple unbalance can be efficiently generated. Therefore, the sizes of the first weight and the second weight can be reduced. In addition, both the weights of the dust collection fan and the motor cooling fan can be reduced.

In one or more embodiment(s), the dust collection fan may be made from light metal. The first weight may be made from heavy metal. According to this configuration, the masses of the dust collection fan and the first weight can be optimized. In other words, the weight of the dust collection fan can be reduced, and the weight and the size of the first weight can also be reduced while the function of the first weight is maintained.

In one or more embodiment(s), the first weight may be attached to the dust collection fan by screwing. This configuration facilitates mounting of the first weight and the dust collection fan onto the output shaft.

In one or more embodiment(s), the motor cooling fan may be made from synthetic resin. The second weight may be made from metal. According to this configuration, the masses of the motor cooling fan and the second weight can be optimized. In other words, the weight of the motor cooling fan can be reduced, and the weight and the size of the second weight can also be reduced while the function of the second weight is maintained.

In one or more embodiment(s), the second weight may include a through-hole through which the output shaft extends. According to this configuration, the second weight can be radially positioned with high accuracy. Further, the motor cooling fan is prevented from being deformed due to the centrifugal force applied to the second weight even when the motor cooling fan is made from synthetic resin.

In one or more embodiment(s), the first weight may include a through-hole through which the output shaft extends. According to this configuration, the first weight can be radially positioned relative to the output shaft with high accuracy.

In one or more embodiment(s), the spacer may be in the form of a first bearing rotatably supporting the output shaft. According to this configuration, the bearing originally required to rotatably support the output shaft can be utilized as the spacer, and therefore eliminates the necessity of disposing a spacer additionally. Therefore, the size of the portable electric tool can be reduced and the manufacturing cost can be cut down.

In one or more embodiment(s), the dust collection fan, the motor cooling fan, the first weight, and the second weight may be fixed to the motor shaft by fastening them together. According to this configuration, the manufacturing process can be simplified.

In one or more embodiment(s), the dust collection fan may include a shaft portion extending in the axial direction toward an opposite side from the output shaft and disposed eccentrically with respect to the output shaft. The tool accessory may be fixed to the shaft portion via a second bearing rotatably supporting the shaft portion. According to this configuration, an eccentric circular motion of the tool accessory can be achieved with a simple configuration.

In the following description, an orbital sander (hereinafter simply referred to as a sander) 10 as one exemplary embodiment will be described in further detail with reference to the drawings. The sander 10 exemplarily cited in the present embodiment is also called a finishing sander.

As illustrated in FIGS. 4 and 5 , the sander 10 includes an electric motor 60, a motor shaft 61, and a tool accessory (a sanding/polishing part) 30. One end of the motor shaft 61 is coupled with the tool accessory 30 via another member. As will be described in detail below, the sander 10 is configured in such a manner that the tool accessory 30 performs a processing (sanding, polishing, abrading, etc.) motion by a rotation of the electric motor 60 (the motor shaft 61).

As will be used herein, a direction in which the motor shaft 61 extends is defined to be a vertical direction of the sander 10. One side in the vertical direction on which the tool accessory 30 is located is defined to be a lower side, and the opposite side therefrom is defined to be an upper side. Further, the longitudinal direction of the sander 10 perpendicular to the vertical direction is defined to be a front-rear direction of the sander 10. One side in the front-rear direction on which the tool accessory 30 is located is defined to be a front side, and the opposite side therefrom is defined to be a rear side. Further, a direction perpendicular to the front-rear direction and the vertical direction is defined to be a left-right direction of the sander 10. A right side in the left-right direction when the front side is viewed from the rear side is defined to be a right side of the sander 10, and the opposite side therefrom is defined to be a left side of the sander 10.

As illustrated in FIGS. 1 to 3 , the sander 10 includes a housing 20. The housing 20 includes a front housing portion 21, a grip portion 22, and a rear housing portion 23. The front housing portion 21 and the rear housing portion 23 are coupled in the front-rear direction via a vertically separated forked form, and an upper-side coupling portion functions as the grip portion 22. A power source cord 26 extends out of the rear edge of the rear housing portion 23. The power source cord 26 is used to supply a commercial alternating-current power source to the electric motor 60. The power source of the electric motor 60 may be a battery detachably mounted on the sander 10 instead of the commercial power source.

As illustrated in FIG. 4 , a controller 65 is contained in the lower portion of the rear housing portion 23. The controller 65 is electrically connected to the power source cord 26 and the electric motor 60, and controls the operation of the electric motor 60 by controlling power that is supplied to the electric motor 60. As illustrated in FIG. 1 , a switch 27 is provided at the front portion of the front housing portion 21. The switch 27 is used to perform an operation of starting up and stopping the electric motor 60. The switch 27 is electrically connected to the controller 65.

As illustrated in FIG. 5 , the electric motor 60 is contained in the front housing portion 21. The motor shaft 61 of the electric motor 60 extends vertically, and is rotatably supported by bearings 62 and 63 fixed to the front housing portion 21. The bearing 62 supports the upper end of the motor shaft 61, and the bearing 63 supports the vicinity of the lower end of the motor shaft 61.

A motor cooling fan 40 is disposed below the electric motor 60. The motor cooling fan 40 is fixed to the motor shaft 61 so as to circumferentially surround the motor shaft 61 (the fixation method therefor will be described below). When the motor cooling can 40 is rotated according to the rotation of the motor shaft 61, air is introduced into the housing 20 from outside via intake ports 24 formed on the front housing portion 21 and the grip portion 22 (refer to FIGS. 1 and 2 ). This air passes through the electric motor 60 and flows axially (the direction in which the motor shaft 61 extends), is directed radially outward at the motor cooling fan 40, and is exhausted out of the housing 20 via an exhaust port 25 formed on the front housing portion 21 (refer to FIGS. 1 and 2 ). The electric motor 60 is cooled with the aid of such an air flow.

A dust collection fan 50 is disposed below the motor cooling fan 40. The dust collection fan 50 and the motor cooling fan 40 are axially spaced apart from each other via the bearing 63. The layout of the motor cooling can 40 and the dust collection fan 50 axially spaced apart from each other allows the motor cooling fan 40 and the electric motor 60 to be located closer to each other. Therefore, the motor cooling performance can be improved.

The dust collection fan 50 is fixed to the lower end of the motor shaft 61 so as to circumferentially surround the motor shaft 61 (the fixation method therefor will be described below). As illustrated in FIGS. 5 and 9 , the dust collection fan 50 includes a generally disk-shaped face plate 51, a shaft portion 52, and a plurality of blades 53. The shaft portion 52 protrudes cylindrically downward from the face plate 51 at around the center of the face plate 51. A hole 54 is formed inside the shaft portion 52. The plurality of blades 53 radially extends on the radially outer side with respect to the shaft portion 52 on the lower surface of the face plate 51. A shaft insertion hole 55 is formed on the face plate 51 so as to be in communication with the hole 54. The shaft insertion hole 55 has an inner diameter larger than the hole 54.

The dust collection fan 50 is fixed to the motor shaft 61 in a state that the lower end of the motor shaft 61 is inserted in the shaft insertion hole 55. In this state, the hole 54 of the shaft portion 52 is coaxial with the motor shaft 61, but the shaft portion 52 is eccentric with respect to the motor shaft 61. The shaft portion 52 is rotatably supported by a bearing 64. Therefore, the bearing 64 is eccentric with respect to the motor shaft 61.

A space containing the dust collection fan 50 is in communication with a dust collection passage 28 extending in the front-rear direction in the lower portion of the rear housing portion 23. A dust collection bag 29 is detachably mounted at the rear edge portion of the rear housing portion 23. When the dust collection bag 29 is mounted, the dust collection passage 28 and the inside of the dust collection bag 29 are in communication with each other.

As illustrated in FIGS. 1 and 2 , the tool accessory 30 is located at the lowermost portion of the sander 10, and includes a pad 31 and a base 32 disposed above the pad 31. The pad 31 and the base 32 each have a generally triangular shape pointed on the front side thereof as viewed vertically. As illustrated in FIG. 6 , the pad 31 and the base 32 are coupled via a vertically extending bolt 33. As illustrated in FIG. 5 , a plurality of through-holes 34, which extends through the pad 31 vertically, is formed on the bottom surface of the pad 31 (only one through-hole 34 is visible in the cross-section illustrated in FIG. 5 ). A space 35, which is in communication with the through-holes 34, is generated between the pad 31 and the base 32. This space 35 is in communication with the dust collection passage 28. Sanding paper (not illustrated) is attached to the bottom surface of the pad 31. Holes are formed on this sanding paper at positions corresponding to the through-holes 34 of the pad 31.

When the dust collection fan 50 is rotated according to the rotation of the motor shaft 61, air is introduced into the dust collection bag 29 via the holes of the sanding paper, the through-holes 34, the space 35, and the dust collection passage 28. Dust generated at the time of processing using the sanding paper can be collected into the dust collection bag 29 with the aid of this air flow.

As illustrated in FIG. 5 , the bearing 64, which supports the shaft portion 52 of the dust collection fan 50, is fixed to the tool accessory 30. Therefore, the tool accessory 30 is coupled with the motor shaft 61 via the bearing 64 and the dust collection fan 50. Further, as illustrated in FIGS. 5 to 7 , the tool accessory 30 is further coupled with the front housing portion 21 via a vertically extending connector 70. As illustrated in FIG. 7 , the connector 70 is disposed on each of the front portion and the rear portion of the front housing portion 21.

As illustrated in FIGS. 6 and 7 , each of the connectors 70 includes six foot portions 71, an upper plate portion 75, and a lower plate portion 76 (the number of foot portions 71 is 12 in total). The foot portions 71, the upper plate portion 75, and the lower plate portion 76 are joined as an integrally molded member made from a single material, and the material thereof is TPE (thermoplastic elastomer). The upper plate portion 75 and the lower plate portion 76 each have a rectangular shape elongated in the left-right direction and flat in the vertical direction, and the foot portion 71 has a generally columnar shape extending vertically. The foot portions 71 are unevenly distributed with three of them located for each of the left and right edge portions. The six foot portions 71 are lined up in a row. Each of the foot portions 71 includes a top portion 72, a bottom portion 73, and an intermediate portion 74. The top portion 72 and the bottom portion 73 are conically shaped, and the intermediate portion 74 is columnarly shaped. The upper plate portion 75 is immovably held on the front housing portion 21. The lower plate portion 76 is immovably held on the base 32.

The above-described sander 10 operates in the following manner. First, when the user operates the switch 27 to drive the electric motor 60, the motor shaft 61 starts a rotation. At this time, the bearing 64 coupling the motor shaft 61 and the tool accessory 30, and the shaft portion 52 of the dust collection fan 50 are eccentric with respect to the motor shaft 61 as described above. Therefore, when the motor shaft 61 is rotated, the tool accessory 30 performs an eccentric circular motion (an orbital motion) while changing horizontal relative positions of the top portion 72 and the bottom portion 73 of each of the foot portions 71. At this time, each of the intermediate portions 74 is placed in an inclined posture connecting the top portion 72 and the bottom portion 73. According to relative rotations of the top portion 72 and the bottom portion 73, the inclination direction of the intermediate portion 74 is also rotated while being deformed. In other words, the tool accessory 30 is moved so as to draw a circle along a horizontal surface while keeping this posture without being rotated itself. When the sanding paper attached to the bottom surface of the pad 31 is pressed against a processing target in this state, the processing (sanding, polishing, abrading, etc.) is performed. The dust collection fan 50 includes the eccentric shaft portion 52 and the shaft portion 52 is supported by the bearing 64, by which an eccentric circular motion can be achieved with a simple configuration.

Such an eccentric circular motion of the tool accessory 30 generates a vibration. Therefore, the sander 10 includes a configuration for solving a static unbalance and a couple unbalance with the aid of counterweights (a first weight 80 and a second weight 90), thereby reducing the vibration. In the following description, such a configuration will be described.

As illustrated in FIGS. 5 and 8 to 10 , the first weight 80 is attached to the dust collection fan 50. As illustrated in FIG. 10 , the first weight 80 is generally shaped like a semi-circular plate, and includes an annular portion 81 at the center of the circular arc thereof. The annular portion 81 includes a shaft through-hole 82, through which the motor shaft 61 extends. Therefore, the first weight 80 can be radially positioned relative to the motor shaft 61 with high accuracy.

Further, as illustrated in FIG. 10 , an annular portion 56 is formed around the shaft insertion hole 55 of the dust collection fan 50. The annular portion 56 annularly protrudes from the face plate 51 upward. As illustrated in FIG. 5 , the annular portion 56 is fitted inside the annular portion 81 in a state that the first weight 80 is attached to the dust collection fan 50. According to such a spigot joint structure, the first weight 80 can be radially positioned relative to the dust collection fan 50 with high accuracy.

Further, as illustrated in FIG. 10 , the face plate 51 of the dust collection fan 50 has such a shape that approximately a half of the outer edge portion thereof is bent upward along the circumferential direction. This bent portion corresponds to a portion where the first weight 80 is not attached. Therefore, as illustrated in FIG. 8 , the both circumferential edge portions of the bent portion and the diametrically extending end surface of the first weight 80 are in abutment with each other in the state that the first weight 80 is attached to the dust collection fan 50. Therefore, the first weight 80 can be circumferentially positioned relative to the dust collection fan 50 with high accuracy.

In the present embodiment, the first weight 80 is attached to the dust collection fan 50 by threadably engaging a screw 58 (refer to FIG. 5 ) with a screw hole 57 of the dust collection fan 50 and a screw hole 83 of the first weight 80 (refer to FIG. 10 ). This facilitates the mounting of the first weight 80 and the dust collection fan 50 onto the motor shaft 61. However, the first weight 80 and the dust collection fan 50 may be individual separate members until they are eventually mounted on the motor shaft 61.

The materials of the first weight 80 and the dust collection fan 50 are selected in such a manner that the first weight 80 has a specific gravity higher than the specific gravity of the dust collection fan 50. A centrifugal force required to solve the couple unbalance can be efficiently generated by securing a difference in specific gravity between the first weight 80 and the dust collection fan 50. In other words, the mass of the first weight 80 can be reduced.

In the present embodiment, the dust collection fan 50 is made from light metal (for example, aluminum, magnesium, titan, or an alloy containing any of them). Therefore, the weight of the dust collection fan 50 can be reduced as much as possible while the strength required for the dust collection fan 50, which is subjected to the load of the tool accessory 30, is ensured. Further, in the present embodiment, the first weight 80 is made from heavy metal (for example, iron, zinc, copper, or an alloy containing any of them (for example, yellow brass)). According to this configuration, a large difference in specific gravity can be secured between the first weight 80 and the dust collection fan 50, and the centrifugal force required to solve the couple unbalance can be extremely efficiently generated. This leads to reductions in the weight and the size of the first weight 80. However, the materials of the first weight 80 and the dust collection fan 50 can be selected in any manner as long as the specific gravity of the first weight 80 is higher than the specific gravity of the dust collection fan 50.

As illustrated in FIGS. 5 and 8 to 10 , the second weight 90 is attached to the motor cooling fan 40. The motor cooling fan 40 and the second weight 90 are individual separate members in the present embodiment, but, as long as the motor cooling fan 40 and the second weight 90 are kept in contact with each other inseparably in a state that the motor cooling fan 40 and the second weight 90 are eventually mounted on the motor shaft 61, such a contact state is intended to be included in the state that the second weight 90 is attached to the motor cooling fan 40 herein.

As illustrated in FIG. 10 , the second weight 90 is shaped like a circular sector, and includes an annular portion 91 at the center of the circular arc thereof. The annular portion 91 includes a shaft through-hole 92, through which the motor shaft 61 extends. Therefore, the second weight 90 can be radially positioned relative to the motor shaft 61 with high accuracy. The second weight 90 is disposed at a position opposite from the first weight 80 with the motor shaft 61 interposed therebetween as viewed axially.

Further, as illustrated in FIG. 10 , the motor cooling fan 40 includes a generally partial disk-shaped face plate 41, a plurality of blades 42, and a proximal portion 44. A shaft through-hole 43, through which the motor shaft 61 extends, is formed at the center of the circular arc of the face plate 41. The proximal portion 44 protrudes in a circular arc form from the face plate 41 upward on the radially outer side with respect to the shaft through-hole 43. The plurality of blades 42 radially extends from the proximal portion 44 radially outward on the upper surface of the face plate 41.

As illustrated in FIG. 8 , the proximal portion 44 has a shape in conformity with the annular portion 91 of the second weight 90. Therefore, the second weight 90 can be radially positioned relative to the motor cooling fan 40 with high accuracy. Further, as illustrated in FIGS. 8 and 9 , the both circumferential edge portions of the proximal portion 44 of the motor cooling fan 40 and the both circumferential edge portions of the second weight 90 are in abutment with each other in the state that the second weight 90 is attached to the motor cooling fan 40. Therefore, the second weight 90 can be circumferentially positioned relative to the motor cooling fan 40 with high accuracy.

The materials of the second weight 90 and the motor cooling fan 40 are selected in such a manner that the second weight 90 has a specific gravity higher than the specific gravity of the motor cooling fan 40. A centrifugal force required to solve the couple unbalance can be efficiently generated by securing a difference in specific gravity between the second weight 90 and the motor cooling fan 40. In other words, the mass of the second weight 90 can be reduced.

In the present embodiment, the motor cooling fan 40 is made from synthetic resin. Therefore, the weight of the motor cooling fan 40 can be reduced. Further, in the present embodiment, the second weight 90 is made from metal. The second weight 90 may be made from heavy metal similarly to the first weight 80. According to this configuration, a large difference in specific gravity can be secured between the second weight 90 and the motor cooling fan 40, and the centrifugal force required to solve the couple unbalance can be extremely efficiently generated. This leads to reductions in the weight and the size of the second weight 90. However, the materials of the second weight 90 and the motor cooling fan 40 can be selected in any manner as long as the specific gravity of the second weight 90 is higher than the specific gravity of the motor cooling fan 40. As described above, the motor shaft 61 extends through the shaft through-hole 92 of the second weight 90. Therefore, a reaction force works on the motor shaft 61 in reaction to the centrifugal force applied to the second weight 90, and therefore the motor cooling fan 40 is prevented from being deformed due to the centrifugal force applied to the second weight 90 even when the motor cooling fan 40 is made from synthetic resin.

In the present embodiment, the dust collection fan 50, the motor cooling fan 40, the first weight 80, and the second weight 90 are fixed to the motor shaft 61 by fastening them together. More specifically, as illustrated in FIG. 5 , a screw hole 66 is formed in the motor shaft 61. The screw hole 66 extends from the lower end toward the upper side of the motor shaft 61. The screw hole 66 is in communication with the hole 54 of the dust collection fan 50. The inner diameter of the screw hole 66 is smaller than the inner diameter of the hole 54. Further, a flange 67 is formed on the motor shaft 61. The flange 67 has an outer diameter larger than the inner diameter of the annular portion 91 of the second weight 90, and the flange 67 and the annular portion 91 are axially in abutment with each other. A plate 69 is placed in abutment with the lower edge of the bearing 64 below the motor shaft 61. A conical hole shaped so as to conform with the screw head of a flat-head machine screw 68 is formed at the center of the plate. When the flat-head machine screw 68 threadably engageable with the screw hole 66 is inserted through the hole 54 and the screw hole 66 in this state and tightened, the dust collection fan 50, the first weight 80, the bearing 63, the motor cooling fan 40, and the second weight 90 are axially pressed tightly between the head portion of the bolt engaged with the lower end of the shaft portion 52, and the flange 67. As a result, the dust collection fan 50, the motor cooling fan 40, the first weight 80, and the second weight 90 are fixed to the motor shaft 61. According to this configuration, the manufacturing process can be simplified.

In the present embodiment, the motor cooling fan 40 and the second weight 90 are individual separate members until they are fastened together in this manner, but they may be integrated during the manufacturing process. For example, the motor cooling fan 40 and the second weight 90 may be joined together by fixation using a bolt or may be manufactured integrally by insert-molding.

According to the above-described sander 10, the first weight 80 and the second weight 90 are disposed at axially different positions, and therefore the centrifugal forces respectively applied to the first weight 80 and the second weight 90 can be prevented from being canceled out by each other. As a result, the masses of the first weight 80 and the second weight 90 required to solve the couple unbalance can be reduced. Especially, in the present embodiment, since the first weight 80 and the second weight 90 are axially spaced apart from each other via the bearing 63, a great axial distance can be secured between the first weight 80 and the second weight 90. As a result, the masses of the first weight 80 and the second weight 90 required to solve the couple unbalance can be further reduced.

In addition, the bearing 63 functions as a spacer for axially spacing the first weight 80 and the second weight 90 away from each other. In other words, the bearing 63 originally required to rotatably support the motor shaft 61 can be utilized as the spacer, and therefore eliminates the necessity of disposing a spacer additionally. Therefore, the size of the sander 10 can be reduced and the manufacturing cost can be cut down. However, a spacer may be additionally prepared and disposed between the first weight 80 and the second weight 90.

In the following description, a second embodiment will be described with reference to FIG. 11 . The second embodiment is different from the first embodiment in terms of the fact that a balancer 180 is attached at the lower end of the motor shaft 61 instead of the first weight 80 attached to the dust collection fan 50. The balancer 180 has a center of gravity on the opposite side of the motor shaft 61 from the second weight 90. Such a configuration can also bring about advantageous effects equivalent to the first embodiment because the second weight 90 and the balancer 180 are axially spaced apart from each other. The first weight 80 may be attached to the dust collection fan 50 instead of the second weight 90 attached to the motor cooling fan 40, although this is not illustrated.

In the following description, a third embodiment will be described with reference to FIG. 12 . The third embodiment is different from the first embodiment in terms of the fact that the motor cooling fan 40 and the dust collection fan 50 are not axially spaced apart from each other. The first weight 80 is attached to the lower side of the dust collection fan 50, and the second weight 90 is attached to the upper side of the motor cooling fan 40. Therefore, the first weight 80 and the second weight 90 are disposed at axially different positions. Such a configuration can also contribute to reducing the masses of the first weight 80 and the second weight 90 required to solve the couple unbalance compared to the configuration in which the first weight 80 and the second weight 90 are disposed at the axially same position.

In the following description, a fourth embodiment will be described with reference to FIG. 13 . The fourth embodiment is different from the first embodiment in terms of the fact that a spindle 368 is disposed in parallel with the motor shaft 61. The motor shaft 61 and the spindle 368 are coupled via an endless belt 369 so as to be able to transmit power. The tool accessory 30 is coupled at the distal end of the spindle 368, although this is not illustrated. The motor cooling fan 40 and the second weight 90 are attached at around the upper end of the spindle 368, and a balancer 380 is attached at the lower end of the spindle 368. The balancer 380 has a center of gravity on the opposite side of the spindle 368 from the second weight 90. Such a configuration can also bring about advantageous effects equivalent to the first embodiment because the second weight 90 and the balancer 380 are axially spaced apart from each other.

Having described the embodiments of the present invention, the above-described embodiments are intended to only facilitate the understanding of the present invention, and are not intended to limit the present invention thereto. The present invention can be modified or improved without departing from the spirit thereof, and the present invention includes equivalents thereof. Further, each of the elements described in the claims and the specification can be combined in any manner or omitted in any manner within a range that allows it to remain capable of achieving at least a part of the above-described objects or bringing about at least a part of the above-described advantageous effects.

Further, the above-described embodiments can be applied to not only orbital sanders but also various portable electric tools accompanied by an eccentric circular motion. For example, the above-described embodiments can also be applied to random orbit sanders, polishers, and the like.

The corresponding relationship between each component in the above-described embodiments and each component in the claims will be described below. However, each component in the embodiments is merely one example and shall not limit each component of the present invention. The sander 10 is one example of a “portable electric tool”. The motor shaft 61 and the spindle 368 are one example of an “output shaft”. The tool accessory 30 is one example of a “tool accessory”. The dust collection fan 50 is one example of a “dust collection fan”. The motor cooling fan 40 is one example of a “motor cooling fan”. The electric motor 60 is one example of a “motor”. The first weight 80 is one example of a “first weight”, and the second weight 90 is one example of a “second weight”. However, the second weight 90 and the first weight 80 can also be construed as one example of the “first weight”and one example of the “second weight”, respectively. The balancers 180 and 380 are one example of the “first weight” or the “second weight”. The bearing 63 is one example of a “spacer” and a “first bearing”. The shaft portion 52 is one example of a “shaft portion”. The bearing 64 is one example of a “second bearing”.

DESCRIPTION OF THE REFERENCE NUMERALS

-   -   10 orbital sander     -   20 housing     -   21 front housing portion     -   22 grip portion     -   23 rear housing portion     -   24 intake port     -   25 exhaust port     -   26 power source cord     -   27 switch     -   28 dust collection passage     -   29 dust collection bag     -   30 tool accessory     -   31 pad     -   32 base     -   33 bolt     -   34 through-hole     -   35 space     -   40 motor cooling fan     -   41 face plate     -   42 blade     -   43 shaft through-hole     -   44 proximal portion     -   50 dust collection fan     -   51 face plate     -   52 shaft portion     -   53 blade     -   54 hole     -   55 shaft insertion hole     -   56 annular portion     -   57 screw hole     -   58 screw     -   60 electric motor     -   61 motor shaft     -   62, 63, 64 bearing     -   65 controller     -   66 screw hole     -   67 flange     -   68 flat-head machine screw     -   69 plate     -   70 connector     -   71 foot portion     -   72 top portion     -   73 bottom portion     -   74 intermediate portion     -   75 upper plate portion     -   76 lower plate portion     -   80 first weight     -   81 annular portion     -   82 shaft through-hole     -   83 screw hole     -   90 second weight     -   91 annular portion     -   92 shaft through-hole     -   180 balancer     -   368 spindle     -   369 endless belt     -   380 balancer 

What is claimed is:
 1. A portable electric tool comprising: an output shaft extending in an axial direction and configured to be rotatable; a tool accessory configured to perform an eccentric circular motion according to the rotation of the output shaft; a dust collection fan fixed to the output shaft so as to circumferentially surround the output shaft; a motor disposed on an opposite side of the dust collection fan from the tool accessory in the axial direction, and configured to provide a rotational driving force to the output shaft; a motor cooling fan disposed between the dust collection fan and the motor in the axial direction; a first weight attached to one of the dust collection fan and the motor cooling fan and having a specific gravity higher than the one of the fans; and a second weight disposed at a position different from the first weight in the axial direction.
 2. The portable electric tool according to claim 1, wherein the first weight and the second weight are disposed so as to be spaced apart from each other in the axial direction via a spacer.
 3. The portable electric tool according to claim 1, wherein the dust collection fan and the motor cooling fan are disposed so as to be spaced apart from each other in the axial direction.
 4. The portable electric tool according to claim 3, wherein the first weight and the second weight are disposed so as to be spaced apart from each other in the axial direction via a spacer, and the dust collection fan and the motor cooling fan are disposed so as to be spaced apart from each other in the axial direction via the spacer.
 5. The portable electric tool according to claim 1, wherein the first weight is attached to the dust collection fan and has a specific gravity higher than the dust collection fan, the motor cooling fan is fixed to the output shaft so as to circumferentially surround the output shaft, and the second weight is attached to the motor cooling fan and has a specific gravity higher than the motor cooling fan.
 6. The portable electric tool according to claim 5, wherein the dust collection fan is made from light metal, and the first weight is made from heavy metal.
 7. The portable electric tool according to claim 6, wherein the first weight is attached to the dust collection fan by screwing.
 8. The portable electric tool according to claim 5, wherein the motor cooling fan is made from synthetic resin, and the second weight is made from metal.
 9. The portable electric tool according to claim 5, wherein the second weight includes a through-hole through which the output shaft extends.
 10. The portable electric tool according to claim 1, wherein the first weight includes a through-hole through which the output shaft extends.
 11. The portable electric tool according to claim 2, wherein the spacer is in the form of a first bearing rotatably supporting the output shaft.
 12. The portable electric tool according to claim 1, wherein the dust collection fan, the motor cooling fan, the first weight, and the second weight are fixed to the motor shaft by fastening them together.
 13. The portable electric tool according to claim 1, wherein the dust collection fan includes a shaft portion extending in the axial direction toward an opposite side from the output shaft, the shaft portion being eccentric with respect to the output shaft, and the tool accessory is fixed to the shaft portion via a second bearing rotatably supporting the shaft portion.
 14. The portable electric tool according to claim 2, wherein the dust collection fan and the motor cooling fan are disposed so as to be spaced apart from each other in the axial direction, the dust collection fan and the motor cooling fan are disposed so as to be spaced apart from each other in the axial direction via the spacer, the first weight is attached to the dust collection fan and has a specific gravity higher than the dust collection fan, the motor cooling fan is fixed to the output shaft so as to circumferentially surround the output shaft, and the second weight is attached to the motor cooling fan and has a specific gravity higher than the motor cooling fan.
 15. The portable electric tool according to claim 5, wherein the second weight includes a through-hole through which the output shaft extends, and the first weight includes a through-hole through which the output shaft extends.
 16. The portable electric tool according to claim 14, wherein the spacer is in the form of a first bearing rotatably supporting the output shaft.
 17. The portable electric tool according to claim 16, wherein the dust collection fan, the motor cooling fan, the first weight, and the second weight are fixed to the motor shaft by fastening them together.
 18. The portable electric tool according to claim 16, wherein the dust collection fan includes a shaft portion extending in the axial direction toward an opposite side from the output shaft, the shaft portion being eccentric with respect to the output shaft, and the tool accessory is fixed to the shaft portion via a second bearing rotatably supporting the shaft portion. 